The present invention relates mainly to a belt tensioner, and to a drive system and to an engine including such a tensioner.
It is conventional to place a belt tensioner in a drive system that includes a belt for transmitting motion from a driving pulley to one or more driven pulleys. Such a tensioner generally comprises a device of the piston-and-cylinder type for guiding relative translation between first and second assemblies, the first assembly being secured to a first end of the tensioner and fixed directly or indirectly to the engine block, while the second assembly is secured to a second end of the tensioner and carries a wheel that runs on the belt, the two assemblies being surrounded by a helical return spring urging said assemblies towards a spaced-apart position. Improved tensioners of known types also include hydraulic damping means. Although such tensioners generally give satisfaction, they are relatively expensive. In addition, some embodiments are bulky and/or of limited lifetime. Furthermore, because it has a return spring that is radially on the outside, a conventional type of tensioner has to be fixed via one of its ends. Such fixing is not necessarily the strongest nor the best suited to the small amount of space available in an engine compartment.
Consequently, an object of the present invention is to provide a belt tensioner that is simple in structure.
Another object of the present invention is to provide a tensioner capable of receiving fixing means on any portion of its length.
Another object of the present invention is to provide a belt tensioner that is very reliable and that has a long lifetime.
Another object of the present invention is to provide such a tensioner that is of low cost.
These objects are achieved by a tensioner of the present invention comprising a rigid cage advantageously fitted with fixing means, e.g. for fixing to an engine block or to a plate rotatably mounted on such an engine block.
A rigid part slides in said cage and carries, preferably at one of its ends, means for bearing against a belt, in particular a wheel. Resilient return means urging the cage and the wheel-supporting parts towards a spaced-apart position are mounted inside said part, said means preferably being constituted by a spring, and typically by a helical spring.
Advantageously, the axis of the spring coincides with the longitudinal axis of the rigid cage which itself coincides with the axis of the wheel-carrying part.
Advantageously a layer of self-lubricating material, in particular polytetrafluoroethylene (PTFE), of plastics material, or of elastomer material, is interposed between the cage and the facing face of the wheel-carrying part so as to decrease, increase, or control friction during the sliding of said part in the cage, so as to provide guidance, and friction that serves to damp the tensioner.
The present invention mainly provides a tensioner for a belt, the tensioner comprising:
bearing means for bearing against a drive belt;
an anchor element; and
a resilient return element for pressing the bearing means against the drive belt;
wherein the anchor element comprises a rigid cage for guiding in translation support means for supporting the means for bearing against the belt, and wherein the resilient return element is an element internal to said rigid cage.
The present invention also provides a tensioner, wherein the resilient return element comprises a helical spring disposed inside the support means for the means for bearing against the belt.
The present invention also provides a tensioner, wherein the axes of the anchor element, of the resilient return element, and of the support means guided in translation by the anchor element coincide with a longitudinal axis of the tensioner.
The present invention also provides a tensioner, wherein the anchor element has openings or eyelets for passing fixing bolts.
The present invention also provides a tensioner, wherein the cage is made of sheet metal, and wherein the openings for passing bolts are formed in tabs made by splaying out the sheet metal of the cage by means of is cutouts made in the side walls of the cage.
The present invention also provides a tensioner, including a layer interposed between the rigid cage and the support means so as to provide both guidance and friction to damp the tensioner.
The present invention also provides a tensioner, wherein the intermediate layer is made of elastomer.
The present invention also provides a tensioner, wherein the rigid cage and the support means are substantially rectangular in section.
The present invention also provides a tensioner, wherein the means for bearing against the belt include a wheel.
The present invention also provides a tensioner, including locking means for locking it in a compact storage and mounting condition in which the resilient return element is compressed.
The present invention also provides a tensioner, wherein the locking means comprise a first projecting element secured to the cage, a second projecting element secured to the support means, and a removable coupling part for coupling said projecting elements together.
The present invention also provides a tensioner, wherein the projecting elements include pieces of sheet metal folded from the cage and from the support means, and wherein the coupling part is a pin passing through holes formed in said projecting elements.
The present invention also provides a tensioner, including stroke-limiting means for limiting the stroke of the support means for the means bearing against the belt so as to prevent them from leaving the cage.
The present invention also provides a tensioner, wherein the stroke-limiting means include a sheet metal extension of the cage placed on the path of a projecting sheet metal element of the support means for the means for bearing against the belt.